1. Field of the Invention
The present invention relates to a membrane structure to be applied as a separating agent or a filler or a delivery agent adaptable to a reactive element which performs physical or chemical operations as well as to various separating operations.
2. Related Background Art
Lipids are used as the component of an organism, and a phospholipid is, among the lipids, one of main components of a variety of membrane systems, such as the plasma membrane, the nuclear membrane, the mitochondrion membrane, the Golgi apparatus membrane, and the lysosome membrane, of a cell which forms an organism. Since the phospholipid is an amphipatic molecule having, in the molecule thereof, a hydrophilic group and a hydrophobic group, the water molecules are hydrated in the hydrophilic group and the hydrophobic group is removed from the environment of water if the phospholipid is suspended in a solution. As a result, the hydrophobic groups are aggregated to one another. The form of the aggregation differs depending upon the balance between the hydrophilic groups containing the hydrated water molecules and the hydrophobic groups and determines whether a micelle or a lipid bilayer membrane or a hexagonal structure is formed based on the form of the aggregation. Among the foregoing structures, the lipid bilayer membrane is the basic structure of an organic membrane. The lipid bilayer membrane can be used to artificially form a closed vacuole (liposome) including an aqueous phase. Further, enzyme and membrane-bound protein substance can be, components added to the bilayer membrane. Therefore, the bilayer membrane has been widely used as a model for analyzing the organic membrane, as to substance permeation and information transmission. Further, application to various functional elements has been anticipated. For example, a series of refined enzymes extracted from an organic membrane and embedded in a liposome membrane in order to analyze its function. The orientation with respect to the surface of the membrane is an advantageous means to analyze biological activity of a cell (for example, information receipt, energy conversion, active transportation and biosynthesis) which is a complicated membrane system involving a multiplicity of intracellular organelle. Actually, the fact that the energy conversion mechanism in a mitochondrial inner membrane conforms to a chemiosmotic hypothesis has been proven from an experiment using a model of conjugated reconstitution of bacteriorhodopsin and an ATP synthase (Racker, E. and Stoeckenius, W.: J. Biol. Chem., 249, 662-663 (1974)).
Further, engineered application of the foregoing reconstitution is exemplified by a technology using bacteriorhodopsin and disclosed in Japanese Patent Laid-Open No. 61-124384. That is, the foregoing system has a structure arranged in such a manner that refined bacteriorhodopsin extracted from halophile and the ATP synthase are held by a liposome membrane. By arbitrarily determining the outer and inner conditions of the liposome and by applying visible rays, the function of the bacteriorhodopsin held by the membrane causes protons to be transported from the aqueous phase on the outside of the liposome to that in the liposome. As a result, the electrochemical potential (membrane potential) of the proton is generated across the liposome membrane. By previously supplying ADP and inorganic phosphoric acid to the aqueous phase on the outside of the liposome, the ATP synthase allowed to co-exist in the membrane is able to use the electrochemical potential to synthesize ATP from the ADP and the inorganic phosphoric acid. By disposing luciferase in the aqueous phase on the outside of the liposome, light can be emitted due to decomposition of luciferin using the synthesized ATP.
Since the liposome is able to hold a water soluble substance in the internal aqueous phase thereof, an application as a drag delivery capsule, such as a microcapsule, has been anticipated.
Another attempt has been made to develop a lipid membrane simulated to an organic membrane by, in an engineering manner, using the self-organizing characteristics of the lipid. The foregoing attempt is characterized by: membranes in each of which there is a monomolecular membrane of lipid (a Langmuir membrane: an L-membrane) developed on the interface between gas and liquid which are, as flat membranes, transferred onto a substrate where they are stacked (Langmuir-Blodgett film: LB film); a membrane (a black membrane: BLM) in which a bimolecular membrane of lipid is formed in each aperture formed in a partition plate disposed in a water solution; and a cast membrane. A suggestion has been made that a stable lipid membrane is, by the LB method, formed to have a flat structure by combining high molecular gel and a bimolecular membrane of lipid (refer to Japanese Patent Laid-Open No. 5-7770).
As a method of providing a desired physical or chemical function to the lipid membrane, a method can be used using functional lipid molecules as the component of the membrane and a method causing the functional molecules required to obtain a desired physical or chemical function to be held in the lipid membrane or on the lipid membrane. For example, it is exemplified by a structure formed by causing an organic metal complex (ferrocene, a ruthenium complex or a phthalocyanine complex) or a functional pigment (a squallyrium derivative) having a synodic body forming ability to be held in the membrane or a structure using an amphipathic compound or a high molecular compound having a plurality of functional groups of atoms as the material of the membrane.
As an example of developed organic functional elements using a protein substance, an attempt has been made to arrange functional molecules to be stacked in 3D manner by introducing, into the monomolecular membrane of lipid, a ligand capable of singularly bonding with a protein substance (Refer to Uzgiris, E. E., Krongrg, R. D.: Nature, 301, 125-129 (1983)).
Another attempt has been made which has an arrangement that particles having lipid membrane layer formed on the carrier thereof are used to separate the organic substance (refer to Japanese Patent Laid-Open No. 3-502836).
The high standard function of an organism is achieved by cooperation of plural kinds of enzymes. A conventional lipid membrane has been used only as the field for reconstituting hydrophobic enzymes among a multiplicity of enzymes of an organism that can be carried by the membrane. To apply the high standard functions of an organism in an engineering manner, a structure is required that links the function of the organic membrane and the function of the water soluble molecule. Furthermore, the organic membranes are differentiated depending upon their functions in a variety of systems (the plasma-membrane, the nuclear membrane, the mitochondrion membrane and the endoplasmic membrane). Moreover, the water soluble molecules included in the membrane system differ depending upon the type and the concentration. The foregoing fact is an important factor to prevent feedback inhibition in the multi-stage enzyme reaction to cause the reactions to proceed as desired. Therefore, the simulation system of the functions of an organism must have a structure arranged such that the functional molecules are individually sectioned with adequate concentrations. From the foregoing, problems experienced with the conventional structures are as follows.
Liposome presents a problem in that membranes having different components cannot be stacked. What is worse, the membrane suffers from unsatisfactory strength, causing a problem to arise in that a large area membrane cannot easily be formed.
A flat membrane of a type manufactured by the LB method as disclosed in Japanese Patent Laid-Open No. 5-7770 exhibits a capability of forming a large area membrane but lacks the fluidity of the membrane. This is because the mutual reactions due to the diffusion and collision of molecules in the membrane surface have been interrupted. Since the foregoing flat membrane is a secured membrane, another problem arises in that the mutual reactions of molecules held in the individual membrane surfaces have been interrupted. Since the lipid bilayer membrane manufactured by the LB method is formed into a flat shape, the number of types of the lipid membranes that are able to co-exist in one water solution must be two or less.